Created on:2021-06-28 11:48

Hydraulic fault diagnosis and maintenance of shears

Hydraulic fault diagnosis and maintenance of shears

As a kind of billet cutting device, hydraulic shear has been adopted by many enterprises because of its light weight, small volume, less investment, short cutting cycle and safe use.

(1) Problems and analysis of shears

The hydraulic cylinder control part of the hydraulic shear used in a factory is shown in Figure R. The system uses throttle valve as back pressure valve for buffer. Theoretical analysis shows that the scheme is simple and feasible. The throttle valve throttles the oil discharged from the hydraulic cylinder to reduce the running speed of the piston, so as to play a buffer role and avoid impact. However, the vibration of the system is large in use. Vibration leads to the decrease of reliability and life of system components, the loosening of connecting bolts, the cracking of pipes and the failure of the whole system to work normally. Hydraulic shock is one of the main reasons for the vibration of the system. The reason is that the back pressure buffer of throttle valve is improper.

Although the orifice of the throttle valve is adjustable, it remains unchanged in the buffering process. When there is a force, the piston speed can not be reduced to zero, but can only tend to a constant value, so the mechanical shock always exists. It shows that using the throttle valve as the back pressure buffer element can not completely eliminate the shock, thus causing the system vibration.

The area ratio of rod cavity and non rod cavity of hydraulic cylinder is S1: S2 = 1:2.82. Without any loss, p2s2 = n + P1s1, n is the load shear force. When the slab is cut suddenly, n = O, p2s2 = P1s1, P1 = 2.82p2, which is much larger than the reasonable pressure difference of throttle valve 0.2 ~ 0.3MPa. Because of the large pressure difference between the front and back of the throttle valve, the energy loss also increases. All the lost energy is converted into heat. After being absorbed by the oil, the temperature of the oil will rise when it passes through the orifice, which will aggravate the deterioration and oxidation of the oil, precipitate various impurities, cause blockage, cause blockage of the throttle valve, and cause vibration of the system.

Although it is improper to use throttle valve as back pressure buffer in the hydraulic system of shearing machine, if the throttle valve is simply removed, it will inevitably lead to the aggravation of hydraulic shock and vibration.

(2) Application of back pressure buffer circuit of sequence valve

According to the actual use of hydraulic shears in production, it can be seen that the reversing of hydraulic cylinder is frequent, and the instantaneous flow mutation and pressure impact often occur in the hydraulic system. In order to improve the working performance of the hydraulic system and reduce the impact and vibration, the back pressure element is changed from throttle valve to sequence valve, and the hydraulic cylinder control system is shown in Fig. s. When the shearing machine shears, before the shearing object is clamped, the electromagnetic relief valve is powered on (not shown in the figure), the system pressure rises to 7.5Mpa (2lmpa / 2.8 = 7.5Mpa), the sequence valve is closed, the system realizes differential, and the shearing speed is accelerated; When the sheared object is clamped, the system pressure rises more than 7.5Mpa, the sequence valve opens and does not produce back pressure. The system pressure continues to rise and the sheared object is cut off. Then the system pressure drops and the sequence valve closes to produce back pressure and form buffer.


(3) Summary

Using sequence valve makes the system in random back pressure state, reduces the pressure loss and slows down the vibration. At the same time, it also eliminates a series of problems caused by the large pressure difference between the front and back of the throttle valve.

After adopting the above scheme, the shearing machine has good operation effect and obvious economic benefit.

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